1. Field of the Invention
The present invention relates to a method and apparatus for managing a physical channel in a mobile communication system. More particularly, the present invention relates to a method and apparatus for managing a Supplemental CHannel (SCH) in a Code Division Multiple Access (CDMA) system for providing a data communication service.
2. Description of the Related Art
Current mobile communication networks provide a high-speed data service in addition to a traditional voice service. A high-speed data service enables a multimedia service which includes the transmission of moving pictures as well as e-mail and still images through mobile terminals. Exemplary mobile communication systems that support the high-speed data service include the synchronous CDMA2000 1x system and asynchronous Universal Mobile Telecommunication System (UMTS). A mobile communication system that supports the multimedia service transmits packet data having different properties than traditional voice data.
For example, packet data is bursty unlike voice data. Therefore, instead of having a continuous stream of a constant amount of data, as is the case with voice data, packet data typically occurs in short bursts of a large amount of data. Accordingly, the mobile communication system additionally assigns an SCH as well as a Fundamental CHannel (FCH) as traffic channels in order to stably transmit a burst of packet data. A mobile station (MS) and a base station (BS) each have a module for managing radio resources including network-specified channels like the FCH and the SCH.
FIG. 1 illustrates a simplified configuration of a conventional mobile communication system using the SCH. Referring to FIG. 1, an MS 10 and a BS 20 wirelessly communicate on channels in accordance with wireless communications standards. For this purpose, radio resource managers 11 and 21 in the MS 10 and the BS 20 assign and/or release radio channels, including the SCH, and provide control for the radio resources of the MS 10 and the BS 20. In particular, the radio resource controller 11 of the MS 10 controls the operation of receiving an SCH assignment message from the BS 20 and receiving data on an assigned SCH for a predetermined period of time.
FIG. 2 is a flowchart illustrating an SCH managing method in a conventional mobile communication system. This procedure is carried out in the radio resource manager 11 of the MS 10 illustrated in FIG. 1.
Referring to FIG. 2, upon the generation of a burst of packet data to be transmitted to the MS 10, the BS 20 transmits an SCH assignment message to the MS 10 on an FCH in order to assign an SCH to the MS 10. The SCH assignment message is known as Supplemental Channel Assignment Message (SCAM) in an IS-95B system and as an Extended SCAM (ESCAM) in an IS-2000 system. Upon receipt of the SCH assignment message in step 201, the MS 10 determines whether it is time to receive data on an assigned SCH in step 203.
The SCH assignment message typically includes information about an assigned time for data transmission on an SCH and a duration for which the data transmission is valid. If the assigned time has come in step 203, the MS 10 receives data from the BS 20 on the assigned SCH in step 205. In step 207, the MS 10 determines whether the duration has expired during the data reception. The data reception continues during the duration. Upon expiration of the duration, the MS 10 releases the SCH and ends the data transmission in step 209.
Meanwhile, to make the burst data transmission efficient, after transmitting an SCH assignment message to the MS 10, the BS 20 transmits another successive SCH assignment message before the duration expiration. The MS 10 receives the new SCH assignment message before the duration expiration of the assigned SCH and if it is determined that the SCH is again assigned, the MS 10 continues receiving burst data during a new duration. If the duration of the assigned SCH expires before receiving the new SCH assignment message on the FCH, the MS 10 releases the existing SCH and ends the burst data reception.
As described above, SCH assignment depends predominantly on the transmission of the SCH assignment message on the FCH. After transmitting an SCH assignment message, the BS transmits burst data on an assigned SCH during a duration that begins with the assigned time. Radio Configuration (RC) 3 or above, which defines the SCH, provides that a Frame Error Rate (FER) is maintained at or below a predetermined level through forward power control, and the FCH errors at all times are at or below a level set by the BS. RC 3 is a radio configuration provided in C.S0002-C v1.0 for the reverse power control sub-channel in CDMA2000 1x, the entire contents of which is hereby incorporated by reference.
In the case where the MS fails to receive the SCH assignment message on the FCH due to transmission errors, the BS still transmits burst data on the SCH at the assigned time because it has already transmitted the message. However, the MS cannot receive the burst data until after receiving the next SCH assignment message. Thus, the MS requests a retransmission of data to the BS with sequence numbers that it has not received and the BS correspondingly retransmits the data. As a result, the efficiency of the whole system and data reception throughput are decreased.
Accordingly, there is a need for an improved method and apparatus for managing a physical channel in a mobile communication system that doesn't decrease system efficiency or data reception throughput when an MS failed to receive the SCH assignment message on the FCH due to transmission errors.